The present invention relates to Electromagnetic actuators and in particular electromagnetic solenoids such as those employed for water inlet valves used in household appliances. Electromagnetic actuators of this type typically employ a pole frame formed of ferro-magnetic material which surrounds or extends over the outer periphery of an electrical coil with a tubular ferro-magnetic pole piece member connected thereto which extends into the inner region of the coil. The tubular pole piece member has a moveable armature received therein and, in applications such as water valves, employs a non-magnetic member slidably guiding movement of the armature within the pole piece.
Heretofore, the tubular pole piece has been attached to the pole frame by press fitting the end of the pole piece into a circular aperture provided in the pole frame having closely controlled tolerances for the diameter of the aperture to ensure the press fit. The end of the pole piece member, once press fitted into the pole frame aperture, has been retained therein either by suitable metal deformation such as staking, flaring or by a welding operation.
In such known techniques for attaching a tubular pole piece member to a ferro-magnetic pole frame, it has been found prohibitively costly in manufacturing to provide the tight tolerances on the diameter of the pole frame aperture and to maintain tight dimensional control of the diameter of the tubular pole piece member in order to ensure a press fit of the tubular pole piece member in an aperture in the the pole frame. In addition, the necessity of providing a press fit of the tubular pole piece into the pole frame for temporary retention therein until completion of subsequent staking or welding, has required a separate locating fixture and operational step in the assembly. Thus, it has been desired to find a way or means of attaching a tubular pole piece member to a ferro-magnetic coil frame for a solenoid actuator without requiring tight dimensional tolerances of either part. It has further been desired t provide such an assembly without requiring separate tooling and set-up in the fabrication process to provide location and temporary retention of the pole piece member on to the frame, in preparation for a second or a final operation for securing the pole piece on to the pole frame.